type annotation of files: IO[bytes] -> Protocol with seek and read?

[FynnBe]

First up: I have enjoyed working with httpx a lot and particularly appreciate all the type annotations in it!

Could you please consider replacing the IO[bytes] in the FileContent annotation with a limited protocol for an object supporting read() and seek()?

Motivation

I have a custom BytesReader object that does not implement the complete set of methods required to type check as IO[bytes] with all its flush, close, isatty, etc methods.

I would love to not simply ignore the type checking error (nor to implement a set of methods that are actually not needed).

httpx only uses read and seek (I think)

It seems that in the httpx code this object is handled in the FileField class, specifically in

httpx/httpx/_multipart.py

Lines 203 to 217 in 4fb9528

	def render_data(self) -> typing.Iterator[bytes]:
	if isinstance(self.file, (str, bytes)):
	yield to_bytes(self.file)
	return
	if hasattr(self.file, "seek"):
	try:
	self.file.seek(0)
	except io.UnsupportedOperation:
	pass
	chunk = self.file.read(self.CHUNK_SIZE)
	while chunk:
	yield to_bytes(chunk)
	chunk = self.file.read(self.CHUNK_SIZE)

So you really only require and object with a seek and a read method as far as I can tell. It would be great if this could be reflected in your type annotations...

Potential solution

Using a protocol such as:

import os
from typing import Protocol 

class BytesReaderP(Protocol):
    def read(self, size: int = -1, /) -> bytes: ...

    def seek(self, offset: int, whence: int = os.SEEK_SET, /) -> int: ...